Cardiovascular System and Heart Function

• The heart is a muscular double pump
• It has two main functions: the pulmonary circuit and the systemic circuit

Heart Location and Orientation in the Thorax

• Found between the lungs
• The apex is tilted leftward from the midline
• Situated within the mediastinum from the second to fifth intercostal space
• A healthy heart weighs approximately 250-350 grams

Four "Corners" of the Heart

• Superior Right: At the costal cartilage of the third rib and sternum
• Inferior Right: At the costal cartilage of the sixth rib lateral to the sternum
• Superior Left: At the costal cartilage of the second rib lateral to the sternum
• Inferior Left: Lies in the fifth intercostal space at the midclavicular line

Structure of the Heart: Coverings

• The pericardium has two parts: the fibrous pericardium and the serous pericardium
• Fibrous Pericardium: A strong layer of dense connective tissue which provides support and protection
• Serous Pericardium: Is divided into the parietal layer and visceral layer (epicardium)

Layers of the Heart Wall

• Epicardium: The most superficial layer and the visceral layer of the serous pericardium
• Myocardium: Composed of cardiac muscle arranged in circular and spiral patterns
• Endocardium: A simple squamous epithelium on a layer of connective tissue, which lines the interior of the heart chambers

Chambers of the Heart

• Right and Left Atria: upper chambers that receive blood
• Right and Left Ventricles: lower chambers that pump blood

Internal Divisions

• Interventricular Septum: Divides the two ventricles
• Interatrial Septum: Divides the two atria

External Markings

• Coronary Sulcus: Encircles the heart, separating atria from ventricles
• Anterior and Posterior Interventricular Sulci: Run along the boundaries between the left and right ventricles

Right Atrium

• Forms the right border of the heart
• Receives deoxygenated blood from the systemic circuit through the superior vena cava, inferior vena cava, and coronary sinus
• Internal Features include:
  • Pectinate Muscles: rigid muscles on the anterior wall
  • Crista Terminalis: A landmark used to locate vein entries
  • Fossa Ovalis: A depression in the interatrial septum, remnant of the fetal foramen ovale

Right Ventricle

• Pumps blood into the pulmonary circuit via the pulmonary trunk
• Internal Features:
  • Trabeculae Carneae: irregular muscular ridges
  • Papillary Muscles: anchor chordae tendineae
  • Chordae Tendineae: prevent valve prolapse
  • Pulmonary Semilunar Valve: located at the opening to the pulmonary trunk

Left Atrium

• Receives oxygenated blood from the lungs via pulmonary veins
• Opens into the left ventricle through the left atrioventricular valve (bicuspid or mitral valve)

Left Ventricle

• Features:
  • The apex of the heart
  • Internal Walls: similar to the right ventricle but with thicker myocardium due to the higher force required to pump blood through the systemic circuit
  • Trabeculae Carneae: irregular muscular ridges
  • Papillary Muscles: anchor chordae tendineae
  • Chordae Tendineae: prevent valve prolapse
  • Aortic Semilunar Valve: at the opening to the aorta

Heart Valves

• Atrioventricular (AV) Valves:
• Tricuspid Valve (Right): between the right atrium and ventricle
• Bicuspid (Mitral) Valve (Left): between the left atrium and ventricle
• Semilunar Valves:
• Aortic Valve: between the left ventricle and aorta
• Pulmonary Valve: between the right ventricle and pulmonary trunk

Cardiac Skeleton

• Composed of dense connective tissue surrounding all four valves, providing structural support
• Functions:
  • Anchors valve cusps to prevent overdilation of valve openings
  • Main point of cardiac for cardiac muscle
  • Blocks direct spread of electrical impulses

Function of the AV Valves

• Prevent backflow into the atria during ventricular contraction
• Mechanism:
  • As ventricles fill, the valve flaps hang limply
  • When ventricles contract, papillary muscles contract and chordae tendineae tighten to prevent prolapse

Function of the Semilunar Valves

• Prevent backflow from arteries into the ventricles
• Mechanism:
  • Valves open due to ventricular contraction
  • Valves close as ventricles relax and blood tries to flow back into the ventricles

Heart Sounds

• "Lub-Dup" is the sound of valves closing
• "Lub" is the closure of AV valves
• "Dup" is the closure of semilunar valves

Pathway of Blood Through the Heart

• Oxygen-poor Blood:
• Enters the right atrium via superior and inferior vena cavae
• Flows into the right ventricle and is pumped to the lungs through pulmonary arteries
• Oxygen-rich Blood:
• Returns from the lungs to the left atrium via pulmonary veins
• Flows into the left ventricle and is pumped through the aorta to the systemic circuit

Heartbeat

• Normal Rate: 70–80 beats per minute at rest
• Phases:
  • Systole: contraction phase
  • Diastole: expansion (relaxation) phase

Structure of Heart Wall

• Walls differ in thickness:
  • Atria- thin walls
  • Ventricles- thick walls
• Systemic Circuit:
  • Longer than pulmonary circuit
  • Offers greater resistance to blood flow

Cardiac Muscle Tissue

• Characteristics:
  • Striated and contracts via the sliding filament mechanism
  • Cells are short, branching, with one or two nuclei
• Connections:
  • Intercalated Discs: form complex junctions with adjacent cells
  • Fascia Adherens and Gap Junctions facilitate synchronous contraction

Mechanism of Contraction

• Initiated by the influx of calcium ions into the sarcoplasm
• Signals the sarcoplasmic reticulum to release more calcium, triggering contraction
• Not all cardiac cells are innervated
  • Cardiac cells will contract in rhythmic manner without innervation due to inherent rhythmicity

Conduction System

• Cardiac muscle tissue has the intrinsic ability to: generate and conduct impulses and signal these cells to contract rhythmically
• Conducting System:
  • A series of specialized cardiac muscle
  • Sinoatrial (SA) node sets the inherent rate of contraction

Disorders of the Heart

• Coronary Artery Disease: includes conditions such as atherosclerosis, angina pectoris, and myocardial infarction
• Heart Failure: progressively weakened heart that can lead to congestive heart failure
• Arrhythmias: abnormal heart rhythms including atrial and ventricular fibrillation

Blood Supply to the Heart

• Coronary Arteries: Arise from the base of the aorta and supply the heart muscle
• Coronary Veins: Carry deoxygenated blood from the myocardium to the right atrium

Innervation of the Heart

• Parasympathetic Fibers Decrease heart rate (vagus nerve) and are restricted to SA node, AV node, and coronary arteries
• Sympathetic Nerves: increase heart rate and contraction strength from the cervical and upper thoracic chain ganglia.

Autonomic input

• Controlled by cardiac centers in the reticular formation of the medulla
  • Cardioinhibitory center influences parasympathetic activity to slow heart rate
  • Cardioacceleratory center influences sympathetic neurons to increase heart rate

Explore the cardiovascular system, focusing on heart function. Understand systemic and pulmonary circuits, cardiac muscle contraction, and the role of the SA node. Learn about arrhythmias and heart anatomy.